An improved Peak-to-Average Power Ratio (PAPR) reduction scheme, named Simplified Repeated Clipping and Filtering with Spectrum Mask (SRCF-SM), is proposed for Orthogonal Frequency Division Multiplexing (OFDM) systems, where the schemes of Simplified Repeated Clipping and Filtering (SRCF) and Spectral Clipping (SC) are integrated in the frequency domain, based on the idea of the in-band and out-of-band independent processing. It is shown that the proposed SRCF-SM significantly outperforms the SRCF in PAPR reduction, with very little increase in the computational complexity, which is justified by the simulation results under AWGN channels and QPSK constellation.